I have a water tank which is about 20 meters from the house.
I would like to measure how much water I have inside and I will use SR04T for this.
I already test it, and in-house it is working fine.
Is any possibility to put near the water tank only the sensor and connect it to arduino which will be located in house so around 20 meters from the sensor?
I heard about RS485 but I`m not sure if I need 2 RS485 or only one (in the house). If I need it also from the sensor side, then it needs to be connected to 5V?
I just would like to avoid sending 230V to arduino.
You will need the RS485 module at each end and at least 3 conductor wires (RX TX ground).
May I suggest a wireless method? An RF24l01 radio at each (2 total) end would be about the same price as 2 RS485 modules and would save the expense of wires and stringing the wires. If the water tank is line of sight with no obstructions the range of the radios should be fine.
Wireless method is not an option for me, because this arduino and sensor will be around 50 cm under ground.
Ok, so If I need RS485 on each end, now I think that I need to buy 40V PoE Shield which will power on arduino and sensor will be connected directly to arduino.
Just some suggestions but looking at the sensor there is no way I would want the controller in the house and the sensor 20M away. You can get something as simple as a Nano and place it in a water proof box with the sensor. You can use any protocol you like, but RS485 or CAN would work great for the PHY layer. RS232 if you want to add another conductor. The sensor is sensitive to low voltage but it does not pull much power and the Nano 5V could happily supply its power. Power it with 8 to 12 VDC and it will be fine. The Diode on the Nano will protect you from reverse power. You can add a SEPIC converter to supply the NANO with about 8 - 10 Volts. Hopefully this gives you some ideas. If you want to do it with the Arduino in the house and the sensor in the field use CAN drivers for the control lines. for each wire You need to set them so one is always transmit and the other is receive. You are treating them as simple line drivers. The noise immunity this way will be good.
The pump is also in the water tank, but this is very simple pump without any sensors etc.
I would like start it from the house.
However, so the PoE shield for arduino is not a good idea?
I do not want to use 12v because I was using it for IP camera and after 15 meters from 12V I got 11 or less, 12V is less stable than 40V. Now I have few 40V PoE cameras and everyting is working fine for more than 50 meters (more than 2 years without any error).